Microwave heating apparatus



March 31, 1964 Filed March 13, 1961 S. H. KELLOUGH ET AL v MICROWAVE HEATING APPARATUS 2 Sheets-Sheet 1 21 12 I I I Q MICRO-WAVE l4 GE/VHMTOR r @q; Hui &

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ATTORNEYS.

March 31, 1964 ,s. H. KELLOUGH ETAL 3,127,494

MICROWAVE HEATING APPARATUS Filed March 15, 1961 2 Sheets-Sheet 2 20 2 a l 1 1 n 28 MICROWAVE GENERATOR ATTORNEYS.

United States Patent Ofiice 3,127,494 Patented Mar. 31, 1964 a corporation of Michigan Filed Mar. 13, 1961, Ser. No. 97,407 9 Claims. (Cl. 219-1055) This invention relates generally to microwave hearing apparatus and more particularly to new and improved means for properly concentrating the microwave energy within an oven to provide uniform heating of lossy dielectric articles therein. a

This application is a continuation-in-part of my copending application, Serial No. 49,627, filed August 15, 1960, now abandoned.

It is known to provide relatively fast heating of lossy dielectric articles by the use of high frequency energy in the microwave range. While microwave ovens have been made commercially available in the past, their acceptance by the public has been impeded for several different reasons.

One factor which has proved a problem area in the acceptance of prior art microwave ovens is the difficulty of obtaining proper energy distribution within the microwave oven so as to provide uniform heating and cooking of the lossy dielectric articles therein. Due to the characteristics of microwave energy, it has been found in the cooking of food articles, for example, that the peripheral portions of the food articles tend to be heated at a much higher rate than the center portions, with the result that the center portion is undercooked when the peripheral portion is properly cooked, or alternatively, the peripheral portion must be overcooked to obtain proper cooking of the center portion. In the past, various means have been proposed for evenly distributing microwave power in an empty cavity-such as reciprocating reflector plates, paddle wheel stirrers, eta-but to date no truly satisfactory solution has been found to evenly distribute microwave energy within a lossy dielectric positioned for heating in the cavity.

Accordingly, it is a general object of this invention to provide new and improved microwave heating apparatus for achieving more uniform heating of lossy dielectric articles within an oven.

It is another object of this invention to provide new and improved microwave cooking apparatus, as above, having unique means for concentrating the microwave energy at a desired portion of the food articles to evenly distribute microwave power throughout the food articles and thereby obtain uniform cooking of such food articles.

In accordance with a feature of one illustrative embodiment of this invention, the oven comprises a nonresonant cavity defined by a plurality of walls of electrically conductive material forming a heating chamber and having a door through which the articles of food or other lossy dielectrics to be heated are placed in the chamber. Microwave frequency electromagnetic fields are provided in the heating chamber for cooking thefood articles by means of any suitable high frequency generator coupled to the oven.

Advantageously, the high frequency generator may take the form of a microwave tube having a tubular output probe radiator. The output probe is enclosed in glass or other low loss insulating material and extends into the heating chamber to radiate microwave energy therewithin. Alternatively, the high frequency generator may be coupled to a waveguide which terminates in a microwave radiator inserted in the oven heating chamber through an aperture formed in one of the chamber walls. Preferably, the microwave radiator would be enclosed by a suitable corrosion resistant low loss dielectric housing, such as some types of glass or plastic, to afford protection of the radiator from adverse effects which may arise during the operation of the cooking apparatus.

It is a salient feature of this invention that the microwave energy output from the radiator be concentrated in a particular manner to provide uniform heating of the articles within the oven so as to eliminate the undesirable results of the peripheral heating characteristic of the prior art devices. This highly desirable end is achieved by means of a unique concentrating device positioned about the microwave radiator and its housing.

In accordance with one illustrative embodiment of the invention, the concentrating device comprises an integrally formed tapered concentrator having an opening of relatively large diameter which tapers inwardly from the wall of the oven to an opening of smaller diameter positioned near the output end of the microwave radiator. In the operation of the invention, this tapered concentrator causes the load-such as the food articles to be cookedto be heated in a uniform manner throughout its bulk.

In accordance with a further feature of the invention, the tapered concentrator advantageously may be formed of plastic coated silver plated brass and is secured to the oven wall by welding or by means of corrugated copper foil so as to insure maximum electrical conductivity and contact for optimum efiiciency.

Thus, it is a further object of this invention to provide new and improved microwave cooking apparatus which comprises a tapered concentrator positioned around and operatively associated with a microwave radiator within an oven for achieving uniform heating of an article of food within the oven.

It is a still further object of this invention to provide such a tapered concentrator for a microwave radiator in a microwave oven which is secured to the oven wall by welding or by means of corrugated copper foil so as to assure maximum contact and optimum etliciency of the apparatus.

It is still another object of this invention to provide uniform cooking within a microwave oven by means of a tapered concentrator which is characterized by its relatively low cost of manufacture and its relatively high efficiency of use.

It is a still further object of this invention to provide new and improved microwave cooking apparatus having means for removing steam from the heating chambers, as it is given off by the cooked food articles, through the utilization of a stream of high temperature, low velocity air which has already served to cool the heating components of the oven.

The novel features which are characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following description taken in conjunction with the accompanying drawing in which:

FIGURE 1 is a front elevational view, partly in crosssection, and partly in block diagram form, of a microwave oven incorporating the invention;

FIGURE 2 is a top plan view of one illustrative embodiment of tapered microwave concentrator constructed in accordance with the invention;

FIGURE 3 is a side elevational view, partly broken and partly in cross-section, showing the details of an illustrative embodiment of tapered microwave concentrator in accordance with the invention;

FIGURE 4 is an illustrative view of another alternative embodiment of a microwave oven having a tapered microwave concentrator positioned at the bottom center wall of the heating chamber; and

FIGURE 5 is a view illustrating the method of removing steam from the heating chamber by utilizing a stream of high temperature low velocity air which has already served to cool the heating components'of the oven.

Referring now to the drawing, and more particularly to FIGURE 1, thereof, there is shown one preferable embodiment of microwave oven which for purposes of illustration is depicted with an article of food positioned for cooking therein. Advantageously, the microwave oven 10 comprises a shaped top wall 12, side walls 14, and a bottom Wall 16, all of which define a heating chamber 1 8 therewithin. The particular construction of the oven 10 may take any suitable form or shape as will be apparent to those skilled in the art. In accordance with customary practice, the oven 10 will have a door provided in the front wall thereof for enabling the articles of food 20 to be inserted in cooking position therein.

, As shown in FIGURE 1, the oven 10 is provided with a suitable shelf 22 which is supported by the flanges 25 extending along the side Walls 14 of the oven 10. If desired, the height of shelf 22 may be adjustable, as by providing additional flanges 25 on side walls 14, to enable the articles to be cooked to be positioned at any suitable height, provided the shape of the microwave concentrator is properly related to the selected height to provide uniform cooking of the food articles on the shelf 22.

Advantageously, the top wall 12 of oven 10 is formed with an opening 23, shown in FIGURE 3, through which a microwave energy probe or radiator 24 enclosed within a suitable protective housing 36 is inserted. As known to those skilled in the art, the microwave energy probe 24 may be the output probe of a microwave tube suitably enclosed in a glass, or low loss insulating material housing, or alternatively, the probe 24 may be coupled, by means of a waveguide 26, to a source of microwave energy, such as the microwave generator 28. The details of the microwave generator have not been shown herein since the generator is of a conventional type and may employ any suitable source of microwave energy, such as the magnetron tube or the like.

An article of food to be cooked, such as the lossy dielectric article 20, is adapted to be supported by the shelf 22 within the oven 10. Those skilled in the art will appreciate that due to the inherent characteristics of microwave energy, the articles 20 normally will not be heated in a uniform manner. Rather, there will be a tendency for the peripheral portions of the article 20 to be heated at a much higher rate than the center portion of the article 20 to the end that the peripheral portion of the article 20 will be cooked before its center portion will be cooked.

This is illustrated in FIGURE 1 of the drawing, wherein the article 20 is divided by the dotted lines into a peripheral portion P and a center portion C. In practice, it has been found that the portion P will be heated almost exclusively and the portion C will be raw or greatly undercooked at the time when the portion P is sufliciently cooked or heated.

This highly undesirable result is eliminated in accordance with a novel feature of this invention by the provision of a unique tapered concentrator 32 positioned about the microwave energy probe 24. As shown in greater detail in FIGURES 2 and 3 of the drawing, the tapered concentrator 32 comprises a plurality of tapered walls which are joined to form a rigid unitized assembly. The Walls 34 of the concentrator 32 taper downwardly and inwardly from an opening of relatively large cross-section at the upper portion of the concentrator 32 to an opening of small cross-section at the lower portion of the concentrator 32.

The upper and lower openings defined by the concentrator walls 34 advantageously are coaxially aligned and the protective housing 36 for the microwave energy probe 24 is positioned through said openings. In the operation of the invention, the tapered concentrator 32 serves to focus or concentrate the microwave energy output of the radiator probe 24 towards the center portion C of the article of food 20, thereby compensating for the normal faster heating rate at the peripheral portion P thereof. As a result, the heat distribution is uniform throughout the article 20 and it will be cooked in an even and uniform manner.

It is important that the microwave energy tapered concentrator 32 be made rigid and highly conductive. To this end, in one illustrative embodiment of the invention, the walls of the tapered concentrator 32 are formed of silverplated brass and the concentrator is secured or mounted to the upper wall 12 of the oven 10 in a manner to provide maximum contact between the concent'rator 32 and the oven. Since the surface of the silverplated brass concentrator may tarnish and alter the heating pattern, it advantageously may be encased in a low loss, electrically transparent plastic material.

In accordance with a feature of this invention, each of the tapered walls 34 of the concentrator 32 is provided with a horizontally extending flange 38 which is fastened to theupper wall 12 of the oven 10 as by means of a suitable fastener such as the threaded bolts 40 and nuts 42 associated with each flange 38.

The contact between the flanges 38 of the tapered concentrator and the wall 12 of the oven 10 advantageously is optimized by means of welding or alternatively by means of a corrugated metal sheet material, such as the copper foil 44, which is positioned between each flange 38 and the wall 12 of the oven 10.

It will be appreciated by those skilled in the art that normally the junction of the flanges 38 and the oven wall 12 will not necessarily assure maximum contact therebetween due to bends, imperfections, indentations and the like which may be present in the structures. Thus, it is useful to either weld the flanges to the oven wall or t'oprovide corrugated copper foil between the flanges 38 and the wall; 12, which foil will be compressed when the bolts 40 and nuts 42 are tightened to provide maximum contact between'the flanges and the oven wall.

In addition tothe above features, it is contemplated that the loading adjustment or the microwave generator to load coupling may be varied by properly selecting the cross-section of the tapered concentrator 32. If the transverse eross-section of the tapered concentrator 32 is adjusted so that the tapered Walls G ltare either nearer to or further from the input probe 24-, the tube-to-load coupling maybe varied, thereby varying the microwave power input to the load.

In one particular embodiment of microwave concentrafor which has been constructed and operated successfully in a microwave oven, microwave energy at a frequency of 2,450 megacycles was supplied from the microwave generator source and the concentrator to deliver about 1 ,000 watts of power to the load, and approximately four times as much power/cubic inch was delivered to the center volume C of the food article 20 as was delivered to the peripheral portion P thereof. This served to compensate for the inherent tendency of the microwave oven to heat the peripheral portion at a faster rate, and uniform cooking of the article of food 2t was achieved.

In a particular illustrative embodiment, wherein the tapered concentrator comprised tapered walls 34 of approximately one inch in length and wherein the bottom opening of the concentrator measured approximately 3% inches across, and wherein the angle of taper was ap-' proximately 25 degrees, a piece of meat approximately 6 inches by 8 inches in area was cooked in uniform manner with the power energy output being concentrated at a 3 /2 inch square central portion thereof.

Those skilled in the art now will appreciate that the microwave concentnator may be shaped in a manner other than as illustrated herein in accordance with the principles of the invention. Thus, a microwave concentrator of parabolic or modified parabolic form might be used to provide the uniform heating results described above.

It further will be appreciated by those skilled in the art that the microwave concentrator may be positioned in walls of the oven other than the top wall installation shown in the illustrative embodiment of FIGURE 1. Thus, FIGURE 4 of the drawing is an illustrative view of another alternative embodiment of the invention having the novel tapered concentrator described hereinabove positioned at the bottom wall of the heating chamber.

This bottom mounted embodiment is of particular advantage in certain microwave oven constructions where a top wall installation may result in a degree of power concentration which is highly sensitive to the dimensions and taper of the concentrating wave guide. In accordance with a feature of this invention, this sensitivity and any undesirable effects resulting therefrom are avoided by locating the microwave input probe and tapered concentrator walls at the bottom of the heating chamber.

As shown in FIGURE 4 of the drawing, the microwave oven is formed with the top wall 50 and side walls 52, with no openings in top wall 56* of the type shown in the previous figures. However, the bottom wall 54 of the oven is formed with an opening 56 through which a microwave energy probe 2 i, enclosed within a suitable protective housing 36, is inserted. In the manner set forth in detail hereinabove, the microwave energy probe 24 and its housing as are enclosed by a tapered concentrator 32 to focus or concentrate the microwave energy output of the probe 24 towards the center portion C of the article to be heated within the oven chamber. Due to the advantageous characteristics of the concentrator 32, as explained above, the heat distribution throughout the article 20 is uniform and the article at will be cooked in an even and rapid manner.

Advantageously, the microwave oven may be provided with support rods 59' which extend longitudinally along the side walls 52 of the oven for supporting a suitable shelf 58, formed of Pyrex or the like, upon which the article of food 20 is positioned. Manifestly, the height of the shelf 58 may be adjustable, as by providing a plurality of spaced support rods 59 on the side walls 52, to enable the articles of food to be positioned at a desired height relative to the microwave concentrator and probe assembly.

In the actual manufacture and use of microwave ovens constructed in accordance with the illustrative embodiment of FIGURE 4, it has been found that the degree of power concentration is not as sensitive to the dimensions and taper of the concentrating wave guide as that which may be present in some top wall concentrator mountings. As a result, the manufacturing tolerances of the microwave concentrator are not particularly critical and the microwave oven is not limited to any particular dimensions and taper of the concentrator, or to any particular dimensions and slope of the oven cavity walls.

In accordance with a still further feature of this invention, the microwave oven may be constructed in such a manner as to permit the steam given off by the cooked articles to be removed from the cavity in a highly efficient and economical manner. Thus, as shown in FIGURE 5 of the drawing, the microwave oven may take the form generally described hereinabove with respect to the prior embodiments wherein the oven is formed by a top wall 50, side walls 60 and 61 and bottom wall 54. In this case, side wall 60* may be the front wall of the oven which is selectively operable, as at the hinged connection 69. Bottom wall 54 is formed with a suitable opening 56 through wihch a microwave energy concentrator 32 is positioned. The microwave radiating probe is coupled to a suitable microwave generator 28 for enabling microwave energy to be distributed in an advantageous manner in the microwave oven for uniform cooking of the article 20 supported on the shelf 58.

In this embodiment, it will be noted that the microwave generator 28 is positioned within a lower components chamber :62 defined by the walls '64, 65 and 66 beneath the heating cavity of the microwave oven. An air intake opening 68 is provided in the front side wall 64 and an air outlet opening 70 is provided in the rear side wall 65. The air outlet opening 7E1) is coupled by means of a suitable conduit 72 to an opening 74- in the microwave oven chamber. In addition, the front wall 60 of the microwave oven chamber is provided with an air routlet opening 76 to define an air flow path through the lower chamber past the microwave generator 28, up through the conduit 72 and across the microwave oven cavity for exit at the opening 76.

In the operation of this particular embodiment of the invention, the air taken in through the opening 68 in the components chamber 62 passes the microwave generator 28 and its associated components to cool the latter and to reduce the heat generated thereat. This stream of low velocity, low temperature air becomes a stream of low velocity, high temperature air in cooling the microwave generator components, and further serves to remove the steam given ofi by the cooked objects within the microwave oven cavity as the air stream passes through the latter.

Thus, the high humidity air normally present in the heating cavity during the cooking operation is constantly removed by an air stream which has already served to cool the microwave generator components.

It has been found that a microwave oven constructed in accordance with this particular embodiment materially alleviates the problem of water condensation within the microwave oven cavity by the use of the high temperature, low relative humidity, low velocity air stream which sweeps the steam out the front of the oven.

While there has been shown and described a specific illustrative embodiment of the present invention, it will of course, be understood that various modifications and alternative constructions may be made without departing from the true spirit and scope of the invention. Therefore, it is intended to cover by the appended claims all such modifications and alternative constructions as fall within their true spirit and scope.

What is claimed as the invention is:

1. In microwave heating apparatus, the improvement of means for providing uniform heating of articles within a heating chamber comprising a microwave oven formed of a plurality of walls defining a heating chamber, shelf means positioned within said heating chamber for receiving articles of food to be cooked, a probe receiving opening formed in one of said walls, a source of microwave energy, a microwave energy radiating probe coupled to said source of microwave energy and positioned through said opening so as to extend into said heating chamber in heating relationship with the articles of food upon said shelf means, a microwave energy concentrating means positioned within said heating chamber and around said probe for concentrating the energy radiated therefrom to provide uniform cooking of said articles of food, said concentrating means comprising a plurality of tapered walls assembled into a rigid, unitary structure, said tapered walls defining an opening of relatively large cross-section adjacent a wall of the oven and tapering inwardly to an opening of relatively smaller cross-section adjacent the innermost end of said probe. and means for rigidly securing said concentrating means to a wall of said oven.

2. In microwave heating apparatus, the improvement of means for providing uniform heating of articles within a heating chamber comprising a microwave oven formed of a plurality of walls defining a heating chamber; shelf means positioned within said heating chamber for receiving articles of food to be cooked, a probe receiving opening formed in one of said walls, a source of microwave energy, a microwave energy radiating probe coupled to said source of microwave energy and positioned through said opening so as to extend into said heating chamber in heating relationship with the articles of food upon said shelf means, microwave energy concentrating means positioned around said probe for concentrating the energy radiated therefrom to provide uniform cooking of said articles of food, said concentrating means comprising a plurality of tapered walls assembled into a rigid, unitary structure, said tapered Walls defining an opening of relatively large cross-section adjacent a wall of the oven and tapering inwardly to an opening of relatively smaller cross-section adjacent the innermost end of said probe, means for rigidly securing said concentrating means to a wall of said oven, and means for providing optimum contact between said concentrating means and said oven comprising a layer of corrugated copper foil positioned therebetween.

3. In microwave heating apparatus, the improvement of means for providing uniform heating of articles within a heating chamber comprising a microwave oven formed of a plurality of side walls, a bottom wall and a shaped top wall, said walls defining a heating chamber, shelf means positioned within said heating chamber for receiving articles of food to be cooked, a probe receiving opening formed in one of said walls, a source of microwave energy, a microwave energy radiating probe coupled to said source of microwave energy and positioned through said opening so as to extend into said heating chamber in heating relationship with the articles of food upon said shelf means; microwave energy concentrating means positioned around said probe for concentrating the energy radiated therefrom to provide uniform cooking of said articles of food, said concentrating means comprising a plurality of tapered walls assembled into a rigid, unitary structure, said tapered walls defining an opening of relatively large cross-section adjacent a wall of the oven and tapering inwardly to an opening of relatively smaller cross-section adjacent the innermost end of said probe, whereby the cross-section of said concentrating means decreases as a linear function of its height from said relatively large opening to said relatively small opening, means for rigidly securing said concentrating means to a wall of said oven comprising a flange member connected to each of said tapered walls, and fastening means attaching said flange members to the oven walls, and means for providing optimum contact between said concentrating means and said oven comprising a layer of corrugated copper foil positioned between each flange member and the oven wall.

4. In microwave heating apparatus, the improvement of means for providing uniform heating of articles within a heating chamber comprising a microwave oven formed of a plurality of Walls defining a heating chamber, shelf means positioned within said heating chamber for receiving articles of food to be cooked, a probe receiving opening formed in one of said walls, a source of microwave energy, a microwave energy radiating probe coupled to said source of microwave energy and positioned through said opening so as to extend into said heating chamber in heating relationship with the articles of food upon said shelf means, microwave energy concentrating means positioned around said probe for concentrating the energy radiated therefrom to provide uniform cooking of said articles of food, said concentrating means comprising a plurality of inwardly tapered walls assembled into a rigid, unitary structure, means for rigidly securing said concentrating means to a wall of said oven comprising a flange member connected to each of said tapered walls, and fastening means attachingsaid flange means to the oven wall, and means for providing optimum contact between said concentrating means and said oven comprising a thin flexible metal sheet positioned between each flange member and the oven wall.

5. Microwave heating apparatus in accordance with claim 4 wherein said thin metal sheet comprises corrugated copper foil.

6. In microwave heating apparatus, the improvement of means for providing uniform heating of articles within a heating chamber comprising a microwave oven formed of a plurality of walls defining a heating chamber, shelf means positioned within said heating chamber for receiving articles of food to be cooked, a probe receiving opening formed in one of said walls, a source of microwave energy, a microwave energy radiating probe coupled to said source of microwave energy and positioned through said opening so as to extend into said heating chamber in energy heating relationship with the articles of food upon said shelf means, a protective housing of energy transparent material positioned around said probe within the heating chamber, microwave energy concentrating means positioned around said probe and said protective housing for concentrating the energy radiated therefrom to provide uniform cooking of said articles of food, said concentrating means comprising a plurality of tapered walls defining an opening of relatively large cross-section and tapering inwardly to an opening of relatively smaller cross-section whereby the cross-section of said concentrating means decreases as a linear function of its height from said relatively large opening to said relatively small opening, means for rigidly securing said concentrating means to a wall of said oven, and means for providing optimum contact between said concentrating means and said oven comprising a layer of flexible conductive material positioned therebetween.

7. In microwave heating apparatus, the improvement of means for providing uniform heating of articles within a heating chamber comprising a microwave oven having top, bottom and side walls defining a heating cavity, shelf means positioned within said oven for receiving articles of food to be cooked, a probe receiving opening formed in a wall of said oven, a source of microwave energy, a microwave energy radiating probe coupled to said source of microwave energy and positioned through said opening, microwave energy concentrating means positioned within said heating chamber and around said probe for concentrating the energy radiated therefrom to provide uniform cooking of said articles of food, said concentrating means comprising a plurality of tapered walls defining an opening of relatively large cros s-section and tapered inwardly to an opening of relatively smaller cross-section, and means for rigidly securing said concentrating means to a wall of said oven.

8. In microwave heating apparatus, the improvement of means for providing uniform heating of articles within a heating chamber comprising a microwave oven formed of a plurality of top, bottom and side Walls defining a heating chamber, shelf means positioned within said heating chamber for receiving articles of food to be cooked, a probe receiving opening formed in a bottom wall of said heating chamber, a components chamber positioned below said bottom wall, a source of microwave energy within said components chamber, a microwave energy radiating probe coupled to said source of microwave energy and positioned through said opening so as to extend into said heating chamber in energy heating relationship with the articles of food upon said shelf means, a protective housing of energy transparent material positioned around said probe within the heating chamber, microwave energy concentrating means positioned around said probe and said protective housing for concentrating the energy radiated therefrom to provide uniform cooking of said articles of food, means for rigidly securing said concentrating means to a wall of said oven, said means providing optimum contact between said concentrating means and said oven, and means for first passing a stream of low velocity, low humidity air through said components chamber to cool the microwave energy source therein and for then passing the stream of air through said heating chamber to remove the steam therefrom.

9. In microwave heating apparatus, the improvement of means for providing uniform heating of articles within a heating chamber comprising a microwave oven formed of a plurality of top, bottom and side walls defining a heating chamber, shelf means positioned Within said heating chamber for receiving articles of food to be cooked, a probe receiving opening formed in a wall of said heating chamber, a components chamber positioned adjacent said heating chamber, a source of microwave energy within said components chamber, a microwave energy radiating probe coupled to said source of microwave energy and positioned through said opening so as to extend into said heating chamber in energy heating relationship with the articles of food upon said shelf means, a protective housing of energy transparent material positioned around said probe within the heating chamber, microwave energy concentrating means positioned around said probe and said protective housing for concentrating the energy radiated therefrom to provide uniform cooking of said articles of food, means for rigidly securing said concentrating means to a Wall of said oven, said means providing optimum contact between said concentrating means and said oven, an air stream intake opening in said components chamber, an air stream exit opening in said heating chamber, and air conduit means connecting said components chamber with said heating chamber for enabling a stream of low velocity, low humidity air to be passed first through said components chamber for cooling the microwave energy source and then through said heating chamber for removing any steam therein.

References Cited in the file of this patent UNITED STATES PATENTS 

7. IN MICROWAVE HEATING APPARATUS, THE IMPROVEMENT OF MEANS FOR PROVIDING UNIFORM HEATING OF ARTICLES WITHIN A HEATING CHAMBER COMPRISING A MICROWAVE OVEN HAVING TOP, BOTTOM AND SIDE WALLS DEFINING A HEATING CAVITY, SHELF MEANS POSITIONED WITHIN SAID OVEN FOR RECEIVING ARTICLES OF FOOD TO BE COOKED, A PROBE RECEIVING OPENING FORMED IN A WALL OF SAID OVEN, A SOURCE OF MICROWAVE ENERGY, A MICROWAVE ENERGY RADIATING PROBE COUPLED TO SAID SOURCE OF MICROWAVE ENERGY AND POSITIONED THROUGH SAID OPENING MICROWAVE ENERGY CONCENTRATING MEANS POSITIONED WITHIN SAID HEATING CHAMBER AND AROUND SAID PROBE FOR CONCENTRATING THE ENERGY RADIATED THEREFROM TO PROVIDE UNIFORM COOKING OF SAID ARTICLES OF FOOD, SAID CONCENTRATING MEANS COMPRISING A PLURALITY OF TAPERED WALLS DEFINING AN OPENING OF RELATIVELY LARGE CROSS-SECTION AND TAPERED INWARDLY TO AN OPENING OF RELATIVELY SMALLER CROSS-SECTION, AND MEANS FOR RIGIDLY SECURING SAID CONCENTRATING MEANS TO A WALL OF SAID OVEN. 